This invention relates to an idling rpm feedback control method for internal combustion engines, and more particularly to such method which allows the engine to perform stable idling operation immediately after the start of same.
In an internal combustion engine, the engine can easily stall due to a drop in the engine speed when the engine is operated in an idling condition at a low temperature of the engine cooling water or when the engine is heavily loaded with loads by head lamps, air conditioner, etc. in a vehicle equipped with the engine. To eliminate such disadvantage, an idling rpm feedback control method has been proposed e.g. by Japanese Patent Provisional Publication (Kokai) No. 55-98628, which comprises setting desired idling rpm in dependence upon engine load of the engine, detecting the difference between actual engine rpm and the desired idling rpm, and supplying a quantity of supplementary air to the engine in a manner responsive to the detected difference so as to minimize the same difference, to thereby control the engine rpm to the desired idling rpm.
Even if such idling rpm control method is applied, it is difficult to ensure complete combustion of the air/fuel mixture within the combustion chambers of the engine at or immediately after the start of the engine, especially in cold weather, due to low engine temperature, particularly, low temperature of the wall surfaces of the combustion chambers, causing unstable rotation of the engine at engine idle immediately following the start of the engine. Further, since immediately after the start of the engine the battery installed in the engine is charged by the dynamo or generator as it is used for actuating the starter during engine cranking, and the operating dynamo forms a heavy load on the engine, thereby further making the engine operation unstable.
On the other hand, when the engine is started while it has a high temperature, for instance, when it is restarted immediately after operation in hot weather, there can occur bubbles in pipes of the fuel feeding system of the engine due to high temperature. The presence of such bubbles also can result in very unstable rotation of the engine at engine idle, requiring prompt removal of such bubbles.